Unfortunately all this rain & then hot sun tends to make tomatoes crack. Heirloom tomatoes are very thin skinned, and when the sun hits a wet tomato, it can cause the skin to split.
One thing that you can do to help prevent this is pick them a little bit unripe. Look for a slight changing of colour at the bottom or throughout the tomato, this should indicate that it is already ripening inside, and will be delicious to eat in a few days.
Remember, cracked tomatoes does not affect the taste! You can still eat & enjoy the fruit, and if it is starting to rot, you can either simply cut around that part of the tomato or, you can always collect seed from it!!!

When collecting leafy green seeds, pay attention to the plants. They will begin to "bolt", grow upwards & create flowers (they will no longer taste very good at this stage), let those flowers bloom & die back, and then seed pods will form. Let them brown & then collect! Dry further indoors, pop open pods, and there is the seed!

Here are some greens that are sending up their flower stocks, and are about to bloom

Romaine Lettuce bolting, it is about to send out it's flower stock

Romaine sending out flowers

Leafy green flower stocks against a beautiful august evening sky

Red Romaine just about to flower

After the flowers have bloomed, you will have to wait another few weeks for the pods to form and start to dry out . . .watch carefully, when they are ready, they may burst open & you will loose the seed. Take them inside to dry before that stage . . .